Cartridge case



A g, 7, 1945, J. s. SHUIFFLEBOTHAM 2,381,083

CARTRIDGE CASE .Fil ed March 30, 1945.

IN V EN TOR.

JOHN SIDNEY SHUFFLEBOTHAM I HIS ATTORNEY Patented Aug. 7, 1945 John-Sidney Shufllebotham, Walsall, England, as- 7 signor :to Imperial Chemical Industries Limited,

a. icor-poration of Great Britain Application March 30, 1943, Serial No. 481,145

In-Great Britain October 28,1941

6 Claims.

into the cartridge base,'and the cap andanvil are assembled in the cap chamber in a subsequent operation.

- It "has already been proposed to produce cartridge cases by the moulding of at suitable waterproof plastic material, the case being provided with a cavity in the base so that the primeror ignitionmeans maybe vpressed into position in'the samemanner as'is customary in the manufacture oflp'aper cartridge cases. I inherent disadvantage of this method of inserting the ignition means into cartridges formed of plastic material is that the dimensions of thecap chamber and the cavity in the base portion .must .be controlled within very narrow limits, since if the cap chamber .fits too tightly strains will be set up in the base portion-that will tend to increase the possibility of disruption of the case on firing, while if the fitis not sufficiently tight there will not be a .perfectrgas seal between the cap chamber and the base.

It has also been proposed to attach inserts to bodies formed from the thermoplastic material by heating a portion of the said body and then pressing-an unheated insert into the heated portion. This method, however, is unsatisfactory for use in the manufacture of cartridge cases formed from plastics material, for the reason that any heating of the head portion other than purely local to the cap chamber cavity involves a danger of distortion of the case, and such danger must beavoided in view of the small clearances worked to, of the order of a few thousandths of an inch between gun chamber size and the overall dimensions of the case.

I have found that these disadvantages can be overcome, with a consequent increased tolerance in the dimensions of both cap chamber and cavity, thereby facilitating manufacture of the component parts, by forming the case from a thermoplastic material and effecting a localized oftening'o'f 'the cavity walls at the mement-of-iriser tion of thecap chamber;

The present invention therefore comprises moulding the *cartridgecas'e froma thermoplastic material with a cavity in the base slightly smaller in "diameter than the external diameter -o' f"-the cap chamber, heating the-cap chamber to'atemperature greater than "-thefsoftening temperature of the thermoplastic material, pushing the-heated cap chamber into the cavity, and thereafter inserting the cap into the {cap chamber when the latter has cooled.

The difference in diameter between the] cap chamber and thecav'ityin the base is preferably 0.010 to 0.'020inch.

The temperature to which the cap "chamber is heated'is preferably 30to 120 Crhig'her thanthe softening temperatureof the thermoplastic ina terial, provide'd'that it does not exceed the tem perature at which visible 'oxi'dationand tarnishing of the metal of "which *the cap chamber "is composed begins to occur. For the metal commonly used for cap chambers, namely brass, this temperature is about 200.C; and the chambers should therefore .not be heated above 200" C. p

The invention is illustrated by the accompany-j ing drawing, in which Figure 1 represents a longitudinal cross-section of the base of a shotgun cartridge case showing the cap chamber'before the insertion'thereof;

Figure 2 is similar to Figure ,lgbutshowing the cap chamber and primer inserted in position? Referring to the drawing acartridge case 'l fis moulded so that the diameter 'of the cavity'2in the base portion 3 is slightly less (s'hown'in 'eXaggerated manner in Figure 1) than the external diameter of the cap chamber 4. The latter is heated to the required temperature and pressed into the cavity, and the cap 5 and anvil 6 are then inserted in position.

By way of example, a shotgun cartridge case was moulded from a suitably plasticized cellulose acetate composition, the diameter of the cavity in the base portion being formed 0.016 inch smaller than the external diameter of the cap chamber. The latter was heated to 190 C. and was then pressed into the cavity. After cooling the assembly was then completed by the insertion of the primer into the cap chamber.

The present invention is of particular use in its application to the manufacture of cartridges of the smaller types, such as for example small bore shotgun cartridges, in which the liability to the setting up of any deformation strains on pressing in the cap chamber in the cold is proportionately greater than in the case of larger types of cartridges.

Although the invention has been specifically illustrated with reference to a cellulose acetate .composition, it is to be understood that its scope l. The new and improved method of manufacing cartridge cases, which consists in moulding the case of a thermoplastic material with a capreceiving cavity in the base slightlysmaller in diameter than the external diameter of a cap chamber, forming a cap chamberpf material of higher heat resistance than that of the material of the cartridge case, heating the cap chamber to a temperature higher than the softening temperature of the thermoplastic material, forcing the heated cap chamber into the capreceiving cavity in the base of the cartridge case to soften the wall of the cap cavity, and cooling the assembled case and cap chamber to set the thermoplastic material about the cap chamber.

2. The new and improved method of manuf-acturing cartridge cases, which consists in moulding the case of a thermoplastic material with a cap-receiving cavity in the base slightly smaller in diameter than the external diameter of a cap chamber and having a smooth uninterrupted inner wall, forming a cap chamber with a smooth uninterrupted outer wall of metal, heating the cap chamber to a temperature higher than the softening temperature of the thermoplastic material, forcing the heated cap chamber into the cap-receiving cavity in the base of the cartridge case to soften the wall of the cap cavity, and cooling the assembled case and cap chamber to set the thermoplastic material about the cap chamber.

3. The new and improved method of manufacturing cartridge cases, which consists in moulding the case of a thermoplastic material with a cap-receiving cavity in the base slightly smaller in diameter than the external diameter of a cap chamber and having a smooth uninterrupted inner wall, forming a cap chamber of metal and having a smooth uninterrupted outer wall, heating the cap chamber to a temperature higher than the softening temperature of the thermoplastic material, forcing the heated cap chamber into the cap-receiving cavity in the base of the cartridge case to soften the wall of the cap 10 I -a smooth uninterrupted outer wall, heating the cavity, and cooling the assembled case and cap chamber to set the thermoplastic material about the cap chamber.

4. The new and improved method of manufacturing cartridge cases, which consists in moulding the case of a thermoplastic material with a cap-receiving cavity in the base slightly smaller in diameter than the external diameter of a cap chamber and having a smooth uninterrupted inner wall, forming a cap chamber of metal with cap chamber to a degree higher than the softening temperature of the thermoplastic material but below the heat tarnishing point of the metal, forcing the heated cap chamber into the capreceiving cavity in the base of the cartridge case to soften the wall of the cap cavity, and cooling the assembled case and cap chamber to set the thermoplastic material about the cap chamber.

5. The new and improved method of manufacturing cartridge cases, which consists in moulding the case of a thermoplastic-material with a cap-receiving cavity in the base slightly smaller in diameter than the external diameter of a cap chamber and having a smooth uninterrupted inner wall, forming a cap chamber of metal with a smooth uninterrupted outer wall, heating the cap chamber to a temperature from 30 to 120? C. higher than the softening temperature of the thermoplastic material, forcing the heated cap chamber into the cap-receiving cavity in the base of the cartridge case to soften the wall of the cap cavity, and cooling the assembled case and cap chamber to set the thermoplastic mate rial about the cap chamber. U

6. The new and improved method of manuiacturing cartridge cases, which consists in mould: ing the case of a thermoplastic material with a cap-receiving cavity in the base slightly smaller in diameter than the external diameter of a cap chamber, forming a cap chamber of material of higher heat resistance than that of the material of the cartridge case and having an external diameter from 0.010 to 0.020 inch larger than the cavity in the base of the case, heating the cap chamber to a temperaturehigher than the softening temperature of the thermoplastic material, forcing the heated cap chamber into the cap-receiving cavity in the base of the cartridge case to soften the wall of the cap cavity,

and cooling the assembled case and cap chamber to set the thermoplastic material about the cap chamber.

JOHN s. SHUFFLEBOTHAM. 

